(A) Field of the Invention
The present invention relates to a shaft drilling rig, and more particularly to a shaft drilling machine with which a force of rotary drilling and thrust are imparted to at least a drill bit of a drill string to drill a shaft, slush produced due to the drilling is drained together with soil and sand by forward or reverse circulation, and after having drilled the earth to an predetermined depth, a axial portion of the drill string is disconnected and a new sectional drill pipe member is added to the drill string, for further boring the earth.
The shaft referred to herein includes a vertical and inclined ones drilled in the earth.
Also, the shaft drilling rig referred to herein is used for drilling directly a shaft in the earth by the drill string as well as for drilling a shaft inside a steel pipe previously driven into the earth by a pile driver in order to prevent the hole wall from collapsing and also to guide the stabilizer of the drill string.
Said drill string includes two types: One is such that a turning force of drilling and thrust are given to the almost the whole drill string in order to drill the earth, and the other is such that a turning force of drilling and thrust are imparted to only the drill bit for such drilling. Generally, the former type of drill string comprises a swivel joint, kelly bar formed non-cylindrical or square for enabling the transmission of the turning force from a turning drive for the drill string and the axial movement of the drill string, a plurality of drill pipes to be prepared according to the depth of a shaft to be drilled, a stabilizer as a guide member for steady rest of the drill string, drill collar to impart a weight to the drill string, and a drill bit, which are appropriately coupled together. On the other hand, the latter type of drill string which provides for a drilling motion with a turning force of drilling and thrust given to only the drill bit, is generally composed of a plurality of drill pipes to be prepared according to the depth of a shaft to be drilled, stabilizer, drill bit, and means for imparting the turning force of drilling and thrust to the drill bit, which are also appropriately coupled together, and further it is provided, depending upon the solidity of the ground, with a drill collar or gripper which accomodates a reaction to the thrust of the drill string. These members will be referred to as "components of the drill string or drill string components" anywhere in the subsequent text of this specification. Among the above drill string components, tubular ones are so formed as to have a nearly the same inside diameter for the purpose that fluid or slush produced due to the drilling should be smoothly passed therethrough.
The above-mentioned forward circulation method drilling is generally such that a circulating water is fed by a mud water pump into a pipe laid inside or along the drill string, the mud water discharged from below the drill bit to the bottom of the drill hole (shaft) is circulated through between the outer circumferential surface of the drill string and drill hole (shaft) to outside of the drill hole (shaft), and the mud water thus running is utilized to evacuate the sand and water drilled by the drill bit to outside of the drill hole (shaft) while further drilling the earth. On the other hand, the drilling of reverse circulation method is generally such that the slush consisting of mud water is lifted and discharged through the drill string while further drilling the earth. The embodiments of the present invention will be described later with reference to this drilling of reverse circulation method by way of example. However, it will be apparent to those skilled in the art that the shaft drilling rig according to the present invention can be applied to both the forward and reverse circulation methods.
Also the present invention can be applied to a shaft drilling rig of such as type that drill string is supported on frames installed on a leader in order to drill a vertical shaft or inclined one, and to a shaft drilling rig dedicated to drilling of only a vertical shaft and in which the drill string is supported on a crawler or stationary crane, or on a tower, thereby drilling such a shaft.
(B) Description of the Prior Art
Various shaft drilling rigs have been proposed heretofore in the field of art to which the present invention belongs. Among them, an inclined shaft drilling rig taken by way of example will be described with reference to FIG. 1.
As seen from FIG. 1, the prior-art inclined shaft drilling rig comprises a stand 1 which has tiltably installed at the front end thereof a leader 2 by means of a pin 3.
Said leader 2 has a tilt angle adjusted by a tilting means (not shown) and is supported at a tilt angle thus adjusted. The leader 2 has fixed at the top thereof an upper frame 4 for a first frame, and is provided at the front thereof in the direction of width with at least two parallel guide rails 5 which are vertically elongated.
Said leader 2 has disposed at the front thereof a first frame 6 at the upper side and a second frame 14 at the lower side.
Said first frame 6 is so mounted as to be movable vertically along the guide rail 5 by means of a guide member 7 such as rollers. The first frame 6 is suspended from a suspension system, and supports a drill string 16 which will be described in further detail later, and a thrust jack 29 for the drill string 16.
The suspension for said first frame 6 is composed of sheaves 8 and 9 installed on the upper frame 4, hanging block 10, wire rope 11 unwound from a winch (not shown) located on the stand 1 and routed over said sheaves 8 and 9 and hanging block 10, and a wire rope 13 connecting a hanging bracket 12 provided on the top of the first frame 6 with the hanging block 10. This hanging system is so arranged that as the winch is driven, said first frame 6 is adjustable to a desired position as moved vertically along the guide rails 5 on the leader 2.
Said second frame 14 is so mounted as to be movable vertically along the guide rails 5, and supported by a fixing seat 15 provided at the front of the leader 2. Further, this second frame 14 is provided with a holder 30 for the drill string which will be further described later.
Said drill string 16 consists, from the top toward the bottom end, of an upper swivel joint 17 having an albow 17a for connection of a delivery hose, guide pipe 18, lower swivel joint 19, drill pipe 20, stabilizer 21, joint pipe 22, drill collar 23, stabilizer 24, and a drill bit 25, in this order, which all are connected to each other. The guide pipe 18 of the drill string 16 is connected to a rotary drive unit 27 and also so supported as to be movable vertically by a guide 26 located at the bottom end of the first frame 6.
The rotary drive unit 27 for said drill string 16 is so mounted on a seat 28 slidably provided within the first frame 6, as to supply the drill string 16 with a turning force for drilling through the guide pipe 18.
Only one thrust jack 29 for said drill string is shown in the drawing for the simplicity of illustration, but in reality, two parallelly disposed on opposite sides of the drill string 16 and also assembled to the upper half of said first frame 6. The thrust jack 29 is coupled at the moving side thereof with said seat 28 through which it will impart a turning force for drilling to the drill string 16.
Said holder 30 for the drill string is located under the second frame 14. At the time of drilling, this holder 30 is parked in a position away from the location of the drill string 16; when a new drill pipe 20' is added to the drill string 16, the holder 30 is moved to the working position of the drill string 16 so as to temporarily hold the lower half of the drill string 16 disconnected from the drive system.
Here, how an inclined shaft is drilled by the prior-art inclined shaft drilling rig along inside a steel pipe driven in the earth previously by a pile driver (not shown) will be explained along with how to add a drill string component, for example, a drill pipe, to the drill string, with reference to FIGS. 1 to 4.
First, in order to drill an inclined shaft, the leader 2 is tilted correspondingly to a tilt angle .alpha. of the steel pipe 151 previously driven into the earth 150, and the leader 2 is fixed as shown in FIG. 1. Then, the rotary drive unit 27 for the drill string is started to impart a turning force for drilling to the drill string 16. In case of this prior-art inclined shaft drilling rig, the thrust jack 29 is contracted to give a thrust of drilling to the drill string 16. Thus, the drill string 16 is driven down inside the steel pipe 151 as guided by the stabilizers 21 and 24, thereby drilling an inclined shaft 152. During this drilling, the drill slush is lifted up through the inside of the drill string 16 and discharged through the elbow 17a connected to the swivel joint 17. When the thrust jack is contracted and the first frame 6 is lowered, both over a stroke equal to the length of one drill pipe 20, the rotary drive unit 27 is stopped and here a new drill pipe 20' is added to the drill string 16.
In order to add the new drill pipe 20' to the drill string 16, the holder 30 for the drill string 16 is moved to the working position of the latter, so as to hold the drill string. Then, as shown in FIG. 2, the drill string 16 is disconnected at an axial part thereof while the thrust jack 29 is extended, thereby defining between the upper and lower halves of the drill string 16 a space required for the work of adding the new drill pipe 20' to the drill string.
Next, also as seen in FIG. 2, the additional drill pipe 20' is hoisted by a wire rope 32 suspended from a hoisting block 31 with the new drill pipe 20' tilted to an angle equal to the tilt angle .alpha. of the drill string disconnected as described above. Then, the top-end flange 20'a of the additional drill pipe 20' is matched with the bottom-end flange 16a of the upper half, as disconnected, of the drill string 16, as illustrated in FIG. 3. The flanges are connected to each other by bolts (not shown). Here, the wire rope 32 is removed from the drill pipe 20' and the hoisting block 31 is returned to the initial position.
The thrust jack 29 is contracted and the upper half of the drill string 16 to which the new drill pipe 20' has been added, is lowered and the bottom-end flange 20'b of the drill pipe 20' is matched with the top-end flange 16b of the lower half of the drill string 16 as shown in FIG. 4. These flanges are connected to each other by bolts (not shown).
Then, the holder 30 for the drill string 16 is so operated as to release the drill string. Thereafter, the holder 30 is parked at a position away from the location of the drill string 16, and the drill string 16 is supplied again with a turning force and thrust, for drilling, thereby further drilling the earth.
It should be noted that the drill collar 23 is added to the drill string 16 in the procedure having been described above, depending on the rigidity of the earth to be drilled.
With the prior-art inclined shaft drilling rig, however, after an additional drill string component such as drill pipe 20' is carried and hoisted in the air to a location of connection, workers have to manually guide and align the drill string component while it is suspended in the air, to the bottom-end flange 16a of the drill string 16. Therefore, the time of adding any drill string component to the drill string, the workers must support the weight of the component. If the component is very heavy such as the drill collar, considerable labor is required. In this respect, the prior-art inclined shaft drilling rig is not stable in many operations and the work of adding any drill string component is done with a danger. Also, it takes a long time to additionally join a component to the drill string safely and securely. Furthermore, when the drill string 16 is disconnected at an axial part thereof, the upper half of the drill string 16 may possibly turn due to its own weight. Also, immediately after the drill string is disconnected, the first frame 6 may possibly be hoisted up or swing laterally depending upon the tension of the wire rope 11 on the hanging block 10. In these respects, the work of disconnecting the drill string component is accompanied by a very great danger.
Also in case of the prior-art shaft drilling rig, the work of additionally joining a component to the drill string is dangerous and takes a much time since the additional component is joined to the drill string while the component is being suspended in the air by a hanging block and wire rope.